The present invention relates to a feed bar driving apparatus for a transfer press which can selectively perform two-dimensional and three-dimensional feeding of feed bars.
A transfer press is provided with a transfer device which automatically transfers materials to be processed, and this transfer device comprises two feed bars which are arranged parallel to each other and on both sides of the dies in the press, and a feed bar driving device. Two-dimensional feeding is carried out by causing the grip fingers of the feed bars to engage the material to be transferred by first operating the bars to move them toward each other for clamping or gripping the material, then advancing or feeding the material by moving the feed bars in the direction of their length, unclamping and returning the feed bars to the initial position. Three-dimensional feeding, on the other hand, is carried out by adding up-and-down movements or lifting and lowering to the steps of the two-dimensional feeding, and materials are transferred by operating the feed bars to carry out clamping, lifting, advancing, lowering, unclamping and returning.
Unlike the two-dimensional feeding apparatus, because it has only been a short time since the three-dimensional feeding apparatus was first developed, there are few apparatuses among the conventional three-dimensional feeding apparatuses which can transfer materials surely and accurately and at high speed.
As described above, in the three-dimensional feeding operation, up-and-down movements are added to the steps of the two-dimensional feeding, and many of the conventional apparatuses perform both two-dimensional and three-dimensional feeding using a single driving mechanism. In this kind of conventional device, the driving mechanism for carrying out up-and-down movements is incorporated in the mechanism for carrying out the other movements, and thus the device as a whole must be large, requiring a big transfer unit housing.
In recent years, there have been developed presses in which the feed bars have portions that are shorter than the internal length of the press and which have the finger grips thereon, and portions which perform transfer movements and which are connected to the transfer unit housing, and thus the feed bar portions inside the press, i.e., the portions with finger grips, must be drawn outside the press along with the dies when die exchange is to be carried out. When the transfer unit housing is large as described above, it is difficult to draw the feed bar portions which are inside the press out of the press, and further in order to make the portions of the feed bars separable so as to make it possible to draw the shorter ones out of the press with the dies, the press frame must be large, which increases the size between the press columns.
Also, in the conventional clamping and unclamping mechanisms, a rack is provided on each of the carriers which support the feed bars and serves to actuate them to carry out clamping and unclamping movements. The two racks are positioned so that each of them extends toward the other carrier, and they are engaged with a pinion provided between the two carriers. Clamping and unclamping movements are performed by reciprocating the carriers by driving the racks. However, the two racks engaged with the pinion must engage it at a position where the carriers are farthest from each other, and each of these carriers can approach the other only to the point where it runs into the end of the rack of the other carrier which it faces. Thus, there is a disadvantage that clamping movements of the feed bars can be carried out only through a limited distance.